Current answers ara about Gtk2, I am asking about Gtk3.
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neonboyJun 1 '12 at 17:02

I edited the question to better reflect what you seek. Sorry, but the short answer from my research is no, you cannot without having to spend some effort creating a new "hybrid" theme as @Kush explained :( It's not as simple as GTK2 any more.
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izxJun 6 '12 at 6:42

5 Answers
5

Its certainly possible, I don't have much of themeing experience, but when you navigate to /usr/share/themes/*Theme Name*/gtk-3.0/apps/ directory, you'll find .css files, named with apps they target, to theme, so yes you can create the Themes.

Note that the way you mentioned to theme your apps may require some work to be done (like having both Ambiance and Elementary work simultaneously, since every theme has a base file on top of which app specific styling is done, (a file gtkrc in Gtk 2.0 while, a file gtk.css in case of Gtk3.0).

And this base theme file contains styling rules that specifically target the given theme, hence you cannot create Elementary like look and feel from Ambiance's base theme file without making some have changes, and even if you do, you'll loose Ambiance look itself.

Also, in GNOME, it is possible to have only single theme applied at a time, For Example, if you have used Appearance window in Ubuntu 12.04, you know can can select any single theme from the dropdown, in case you have used gnome-tweak-tool, than you can set different themes, for Gtk, Window frames, and icons, but still, it doesn't allow to target specific applications to theme, so as I said earlier, you can set totally different themes for different applications if you cleverly work with base theme file, as of now, no third party applications can do it by itself.

One way you can do it by yourself is that, let the base theme file (gtk.css) have only essential rules which are neutral to any theme, being dark or light. And have the actual theme design written in app-specific files that reside in above mentioned directory, i.e. for styling Nautilus, you can write all required properties in nautilus.css file. Same with every app you wish to target. Obviously, doing such requires some decent Gtk themeing experience.

You may refer this for creating your own theme using template, Also there's a decent documentation on Gtk+ themeing.

I don't want to create a new theme, I want to assign an existing one.
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neonboyJun 1 '12 at 18:38

@neonboy: As I said that with GTK3, its not that simple, a theme is distributed across multiple files, and if dependencies are not satisfied, broken theme is all you'll get. That's why I posted the answer that shows possible solution with GTK3, and not GTK2 (in which doing this is fairly easier).
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KushJun 2 '12 at 3:09

You can use the GTK environment variable GTK_THEME=elementary to launch an app with the elementary theme. For example, running GTK_THEME=elementary pantheon-files will launch the elementary Files app using the elementary GTK theme.

To get this to apply every time you launch a specific app, your best option is likely to create a custom .desktop file (launcher).

Create a custom .desktop file

Open your file browser

Navigate to /usr/share/applications/

Copy the launcher (highlight and Ctrl+C) for the app you want to launch with the elementary theme

Navigate to ~/.local/share/applications/ and paste the launcher (Ctrl+V)

Right-click and open the launcher with a text editor

Modify the line starting with Exec= to include Exec=env GTK_THEME=elementary and then the previous existing contents of the line. (So Exec=pantheon-files would become Exec=env GTK_THEME=elementary pantheon-files)

Save and close the file

The next time you launch the app from Unity (or your app launcher of choice) it will use the elementary theme.

Bonus: make it work when using command line

You may also want the app to launch with the elementary theme when launching it from the command line. To do so:

Nice reply but I cannot get this to work for any theme. Can you give an example using terminal, find /usr/share/themes -type d -name 'gtk-3.0' | awk -F'/' '{print $5}' and gedit for demonstration purposes? E.g. GTK_THEME="HighContrast" gedit or env GTK_THEME="HighContrast" gedit or GTK_THEME=Adwaita:dark gedit... nothing.
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RedsandroJun 25 '14 at 14:21

I just changed it in /usr/share/applications/<appname>.desktop and it worked for me.
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druciferreAug 23 '14 at 3:55

Any way to do this from code inside the app?
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Anony-MousseSep 14 '14 at 15:20

The question is still valid and I found a way: any folder <FOLDER> could be chosen and then a /share/themes/ folder should be created inside it. Afterward any GTK3 theme could be put inside the latter and renamed to the name of the CURRENTLY ACTIVE THEME. At last, this command will make an app use the renamed theme instead of the currently active one:

Look for the exact executable for the program you want to change the theme. for example, if you want it for ooffice then type which ooffice in the terminal.

Look for the bin folder where all applications put their binary executables. Type echo $PATH in the terminal and you will ge the path. I recommend you to create a bin folder in your home directory by typing mkdir ~/bin

Type gedit ~/.bashrc to open your bash rc file.

Go to the bottom of this file and add this line export PATH=~/bin:${PATH}

No we will create a script which will execute your program with custom theme:

It is certainly possible for GTK2 apps using GTK2_RC_FILES env. variable. Also, what themes are you talking about compiling? The question is about systemwide GTK themes available in Ubuntu.
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izxMay 27 '12 at 9:45

1

I believe the method you mentioned targets Gtk2.0 while Ubuntu 12.04 uses Gtk3.0 for themes, so if might not work.
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KushMay 27 '12 at 10:11

You didn't specify that in your original question. Please no antagonise the questioneers.
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Martin Owens -doctormo-Jun 3 '12 at 6:38

4

Originally it was "Can I use different GTK3 themes for individual apps?" wich still had Gtk3 subject in the question, then foss freedom ask me to comment on non valid answers and edit the question if it was necessary, I'm not antagonise anyone.
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neonboyJun 3 '12 at 12:57